In March 2006, the G-20 established a study group on labor mobility and demographics. The World Bank's Social Protection and Labor unit (HDNSP) has been asked to provide an issues note on the relative merits of skilled and unskilled migration, temporary and permanent labor migration, and portability of social security benefits. The objective of this note is: (i) to highlight the relative merits of skilled and unskilled migration for both source and destination countries; (ii) to highlight the relative merits of temporary and permanent migration for source and destination countries; and (iii) to highlight the costs and benefits of enhanced portability of social security benefits and its impact on incentives for migrants and migration outcomes. This issues note comes to the following tentative conclusions. First, highly skilled migration seems to be beneficial for destination countries, but for source countries, highly skilled migration results in a loss of human capital (brain drain). Second, permanent migration seems to be more beneficial for destination countries while temporary and circular migration is more beneficial to source countries. Rather than forcing migrants to return, policies should ease migrants' decision to return by removing obstacles to return migration. Third, enhanced portability of old-age pension and health benefits has important benefits for destination and source countries at reasonable costs. The remainder of this note is organized as follows. The next section explores the relative merits of skilled and unskilled migration. Section 3 provides an investigation of temporary and permanent migration. Section 4 discusses the costs and benefits of enhanced portability, and Section 5 concludes. All tables and figures can be found in the annex.